In order to fine the spring constant of connected parts in bolted joints, many experimental or theoretical researches have been done. But the theoretical and experimental results show a disagreement. As one of the reasons for this, is considered the deformation of a bolt-head which was included in the value regarded as the deformation of the connected parts. And the traditional theoretical researches have been done under the assumption that a uniformly distributed pressure is applied over the bearing surface. In this paper, using the point matching method coupling with the finite element method, a pressure distribution on the bearing surface is made clear as a contact problem of two elastic bodies, and then the deformation of the bolt-head and the connected parts under such a pressure distribution are analyzed and the spring constant are calculated. In addition, the spring constant is measured by experiment. According to the result, the value of the spring constant that was computed by taking account of the pressure distribution of the bearing surface, is not so different from the result under the assumption of a uniformly distributed pressure and Shibahara and other's theoretical value. When the deformation of the bolt-head is taken into account, the theoretical and experimental results show a fairly good agreement.